This invention relates generally to phosphorescent materials.
Materials that are phosphorescent glow in the dark after being exposed to an energy source generating sufficient energy to create phosphorescence. Phosphorescence is the result of electrons associated with molecules changing orbitals in a fashion, which results in the generation of light. Some phosphorescent materials glow after being exposed to energy in the ultraviolet range. Since sunlight may include sufficient ultraviolet energy, sunlight exposure may be sufficient to cause some materials, such as zinc sulfide, to glow.
As one example, zinc sulfide, after having been exposed to ultraviolet light, may emit a pale green light for a period of up to eight hours. Thus, zinc sulfide is utilized in a variety of products including children""s glowing toys and dolls, as well as a variety of non-toy products including signs and safety equipment.
Phosphorescent materials may be provided in the forms of paints, pigments, and films. Many of these films are utilized as lambertian backgrounds to uniformly light displays while others may be used for foreground elements such as shapes or text. Phosphors are available that emit a wide variety of colored light when exposed to energy within a phosphor""s absorption band.
Among the known phosphorescent materials are ZnS (green), CaAl2O4 (blue), SR4Al14O25 (blue-green), SRAl2O4 (green), and Y2O2S (orange-yellow). Each of these phosphorescent materials may emit different wavelengths of light and yet may require different energy levels in order to initiate phosphorescence. Moreover, the period of time that they phosphoresce after being exposed to sufficient energy may vary.
Typically phosphorescent materials are considered xe2x80x9cone wayxe2x80x9d materialsxe2x80x94they may be turned on to phosphoresce. It is then generally considered that these materials will continue to phosphoresce until such time as they reach their ground state. Generally, it is believed that this period of phosphoresce is a function of the characteristics of the material.
Thus, there is a need for better ways to control phosphorescent materials and particularly better ways to control the way that these materials phosphoresce.